First of all (Bastien): A very big share of those cumulated millions(!) of cross-referencing links were/are being imported automatically without even being noticed by editors. In many cases, those also cause double but not identical linkings to sources. F. ex. Echo Nest derives a link to a discogs entry (not for the 1st release) parallel to an editor's manually added one (the 1st).
Although this procedure is probably much more useful for works (and surely appreciated by myself, though others may not care), it by far doesn't guarantee that the automatically derived links to other copyright societies than entered by editors really match - and result in messages like "SHS has additional credit X" etc.
The above also shows the vulnerability of allowing and relying on importing data without preceding examination...
Echo Nest links have been automatically imported for quite some time, already. This, since far more recently, is also the case for Spotify.
As for Echo Nest, it may seem to make sense to a certain extend, at least as long as editors didn't have to (or don't) add external links as sources. The frustrating thing is that Echo Nest is allowed to import additional links in the background and we only find out when adding additional links to sources backing our entries.
Also as those links often don't match as well as our own ones - we invested time on researching - and are already secretly being imported during our own adding process, we should definitely be enabled to evaluate and agree to them or not before they get imported (similar to discogs).
As for Spotify: Is there any logical reason for automatically importing links (no user sees, anyway) to a commercial download portal? As those are being imported without our consent and in no way back up the detailed data we spend time on researching and adding, this procedure actually should be stopped asap.
This also as Spotify listings hardly ever really provide reliable and detailed data, rather to the opposit. F.ex., release dates (if stated at all) go for when having been added to Spotify, no matter if the release was in 1968, etc. To a certain extend, that also goes for iTunes.